As explained in U.S. Pat. No. 5,261,785, the moisture content of the steam, particularly in the later stages of the steam turbine, reaches a level where the moisture should be removed to minimize erosion of the buckets and maintain efficiency of the turbine. One approach to the problem has been to cut back the forward or leading edge of the cover sufficiently to expose the grooves adjacent the tip of the bucket enabling the excess water to be removed from the steam path by the centrifugal action of the buckets. While cutting back the entire forward edge of the cover to permit water removal can be accomplished, the reduction in axial length of the cover negatively impacts the adequacy of the sealing at the bucket tip, i.e. the cover has stationary sealing devices, such as labyrinth brushes or seals, for sealing with stationary components of the turbine.
In the aforementioned patent, that problem is addressed by relieving the cover only at a location adjacent the entrance area of the cover where the cover would otherwise overlie the grooves formed in the bucket adjacent the leading edge. Thus, according to that patent this notched or scalloped area exposes the water removal grooves radially. With only the portion of the cover adjacent the leading edge and the grooves relieved, the balance of the cover may extend its full axial width to essentially overlie leading and trailing edges of the bucket.
While these two approaches can be effective to remove moisture, the cut back or relief in both covers still provides less axial distance to provide adequate sealing at the bucket tip using sealing devices, such as labyrinth or brush seals. One concept advantageously enables the grooves along the bucket to be run out through the tip of the bucket without interference by the cover. However, where the turbine bucket is integrally formed with the cover or when a cover is subsequently applied to the bucket tip after manufacture of the bucket, the grooves along the bucket surface cannot be run out since the bucket cover otherwise interferes with the machining of the grooves. That is, to allow a run out area for the tooling used to machine the grooves as well as to expose the grooves radially, the cover in both cases requires machining back axially or radially beyond the location of the last groove. Accordingly, there has developed a need for moisture removal grooves on integrally covered buckets or buckets having covers installed subsequent to bucket formation but prior to formation of the grooves without the cover being axially cut back or relieved.